Although colorectal cancer is the second leading cause of cancer deaths for men and women in the United States, it would be largely preventable if its precursor lesions were detected and removed early. Most colorectal cancers develop from sessile or pedunculated polypoid neoplasms. Early removal of such neoplasms has been observed to reduce the occurrence of colorectal carcinoma. Colorectal cancer has been observed to develop also in the absence of precursor polypoid neoplasms. Recent studies have indicated that flat or depressed non-polypoid lesions may be the source of such de novo carcinomas. Until recently, non-polypoid lesions were thought to be rare outside Japan, where they are reported relatively often on state-of-the-art optical colonoscopy (OC) examinations. The detection of non-polypoid lesions is challenging, because they tend to be less than 3 mm in height and often imitate normal colonic mucosa or thickened folds. However, when present, non-polypoid lesions have a higher potential for malignancy than do polypoid neoplasms. Although OC has the highest diagnostic accuracy among current methods for examination of the colon, there are concerns about adequate screening capacity and patient adherence to colorectal screening guidelines. Studies have indicated that computed tomographic colonography (CTC) has performance comparable to that of OC in the detection of polypoid neoplasms of clinically significant size. Therefore, primary colorectal screening by CTC followed by optional therapeutic OC could be used to provide adequate screening capacity and maximize patient compliance in large-scale colorectal examinations. However, pilot studies have indicated that CTC tends to miss non-polypoid lesions. Previously, computer-aided detection (CAD), where a computerized scheme detects colorectal lesions automatically and indicates their locations to radiologists, was introduced to maximize the detection accuracy and consistency of CTC examinations. However, most CAD schemes have been designed to detect polypoid neoplasms, and recent pilot studies have indicated that they will need to be adapted for the detection of non-polypoid lesions to reproduce the high detection accuracy that has been reported for CAD of polypoid neoplasms. In this proposal, we will develop a CAD scheme for the detection of non-polypoid lesions in CTC for increasing the accuracy and consistency of radiologists'interpretation in the detection of such lesions. Reliable and consistent detection of non-polypoid lesions would substantially advance the clinical implementation of minimally invasive CTC-based population screening for colorectal neoplasms, thereby increasing patient adherence to colorectal screening guidelines, promoting early prevention of colorectal cancer, and ultimately minimizing the occurrence of colorectal cancer. PUBLIC HEALTH RELEVANCE: We will develop a computer-aided detection (CAD) scheme for the detection of non-polypoid lesions in computed tomographic colonography (CTC) for increasing the accuracy and consistency of radiologists'interpretation in the detection of non-polypoid lesions. The effect of CAD on radiologists'performance will be assessed by use of an observer study. We hypothesize that the application of CAD can provide significant improvement in radiologists'sensitivity for the detection of non-polypoid lesions in CTC. Reliable and consistent detection of non-polypoid lesions would substantially advance the clinical implementation of minimally invasive CTC-based large-scale screening for colorectal neoplasms, thereby increasing patient adherence to colorectal screening guidelines, promoting early prevention of colorectal cancer, and ultimately minimizing the occurrence of colorectal cancer.